| Geological disasters such as landslides, avalanches are frequent in the Three Gorges Reservoir. After the sluice of the Three Gorges reservoir, Water level variation and rainfall will adversely affect on the deformation and stability of the reservoir landslides. Consequently, the study of recurrence mechanism of bedding landslides under water level variation and rainfall in the Three Gorges Reservoir has great theoretical and practical significance.In this thesis, Huangtupo landslide is chosen as the research object. Through the field survey on region of Huangtupo landslide, also the test tunnel in the No.1landslide, we have a better understanding of geological structure characteristics and genetic mechanism of Huangtupo landslide. Obtaining the sliding zone soli in the test tunnel, then the experimental study for macro-characteristics, physico-mechanical characteristics and hydrological properties of the sliding zone soil is taken in order to achieve a basic understanding of the characteristics of sliding zone soil. Then analyzed the monitoring data, to master the deformation and deformed position at this stage, and the impact of the reservoir water level fluctuation and rainfall on the deformation and seepage field of the landslide. The mechanism of the adversely effect of the water level fluctuation and rainfall on landslide is summarized and elaborated from the pore water pressure effects, etc. Based on the above studies, a numerical simulation model of Huangtupo landslide is established for the research of water level fluctuation and rainfall. The changes of the seepage field, stress field, displacement field, the plastic zone and the stability of the landslide is analyzed, then made a comparative analysis of monitoring data. The recurrence mechanism of bedding landslides under water level variation and rainfall is also analyzed. Finally, the landslide prevention measures at the effect water level fluctuation and rainfall is to be taken.According to the research of recurrence mechanism of bedding landslides under water level variation and rainfall, some preliminary results are obtained as follows:(1) Through the test tunnel excavation to expose the geological structure characteristics of No.l landslide, we found that:1. In bedrock of the No.1landslide, the composition of bedrock rock is mainly marl and limestone interbedded, the interlayer sliding belts develop widespreadly;2. Through the main tunnel and the No.3subsidiary test tunnel excavation to expose the geological structure characteristics, the compositon of geological structure are reddish brown gravelly soil, marlite, limestone gravel, block crack rock,, the ground water of slip mass is rich and water seepage is large;3. In the test tunnel, the main sliding zone is discontinuous and develop at multi-bedding. Compared with the pre-survey information, we found that:1.The entire plane range of No.1landslide are roughly the same with the results of the survey by the Hubei Geological Environmental Monitoring Station (2001). At the entrance location of the test tunnel, the geological structure of the entrance location is broken, deformation strongly and is different from the slip mass of the exit position of the test tunnel and the subsidiary test tunnel, so the entrance location are belong to bedrock.2. The location of main sliding zone at the No.3subsidiary test tunnel is in accordance with the survey by the Hubei Geological Environmental Monitoring Station (2001),and the location of main sliding zone at the No.5subsidiary test tunnel is in accordance with the survey by the Changjiang River Commission (2009).The main sliding zone of the No.1landslide is discontinuous, and it has the multi-bedding and bedding creep characteristics.(2) The main sliding zone of the No.1landslide is composed of khaki sliding zone and light grey sliding zone. The results of scanning electron micrograph display that the microstructures of the khaki sliding zone are mainly sheet crystals structures, the light grey sliding zone consist of more silt and sand, the weak layers are mainly granular crystals structures. The content of gravel is higher, the khaki sliding zone soil can be named as silty clay and the light grey sliding zone soil can be named as mealy sand combining with experiment results of the analysis of grain composition. To test fine-grained components of sliding zone soil by using the maximum dry density and the optimum moisture content to control the remolded samples. The parameters of shear strength using the method of saturated fast direct shear test are as follows:C=39.2kPa, Φ=4.8°; C=8.5kPa,Φ=16.1°. The parameters of shear strength using the method of saturated and consolidated slow direct shear test are as follows:C=0.5kPa,Φ=22.0°; C=0.4kPa,Φ=24.2°. The khaki sliding zone soil plays a master role on the deformation and stability of the landslide. The permeability coefficient of slide zone soil are as follows:3.0-8m/s、1.8-7m/s.The two layers of landslide soil are tiny water permeability. The results of the soil-water characteristic curve shows the volumetric water content reduces by a large margin at the initial increase stage of suction matrix. The soil-water characteristic curve of slide zone soil is fitted with Van Genuchten (1980) model, and the fitting effect is good.(3) Analysis from the monitoring data, the deformation of No.l landslide is most intense, the ground movement is in keeping with the deep soil movement, and the displacement of the leading edge of No.1landslide is the largest. The velocity of ground movement is2.57mm/month and the deep soil movement is2.04mm/month.The landslide appears displacement acceleration during the water level fluctuation and rainfall. It shows that the No.1landslide is great influenced by rainfall and reservoir water. The monitoring data of groundwater provide a basis for seepage field of Huangtupo landslide. Through analyzing the variation of monitoring data of water level for borehole ZK4with rainfall and reservoir water since October2010, we found that the groundwater of borehole ZK4is independent of the water level variation, also the rainfall influence is weaker.(4) The No.1landslide combining with the field survey, the test tunnel excavation and the monitoring data, there is strongly compression and deformation in the shallow landslide, the displacement monitoring data of deep borehole show that there is creep deformation both at the main sliding zone and interlayer sliding belts. The No.1landslide creep along the weak interlayer and the contact surface between the soil and bedrock at the long-term influence of tectonism and gravity. The No.1landslide has the multi-bedding and bedding creep characteristics.(5) The impact of reservoir water and rainfall on the landslide are expatiated from the angle of mechanical mechanism. Water level variation and rainfall will affect the seepage field, the change of the pore water pressure lead to the change of the buoyancy and the penetrability, and affect the deformation and stability of the reservoir landslides. At the same time, hydrostatic pressure, the softening and weakening effect of water on the rock mass and the weakening of mechanical parameters of unsaturated soils mechanics are also the important factors for it.(6) The seepage filed, stree field, displacement field, plastic zone of Huangtupo landslide are computed using SEEP/W of the software named Geo-Studio. The results of numerical simulation as follows:①the water level fluctuation have a certain influence in the leading edge of Huangtupo landslide within the range of300meters or less. Away from the reservoir water, the landslide is basically free from the influence of it. There is hysteresis of the phreatic line in the process of reservoir water level fluctuation. The phreatic line is concave when the water level rises and convex when the water level falls. The phreatic line forms a higher head in the leading edge of the landslide when the water level fluctuation. It has a greater impact on the stability of the landslide.②It has an adverse effect on the stability of No.1landslide when the water level is slowly rising from80m to145m.It has a favorable impact on the stability of No.1landslide when the water level is rapid rising from145to175m. It has a more adverse effect on the stability of No.1landslide when the water level is declining from175m to145m. At the same time, it has an adverse effect on the stability of leading edge of No.1landslide when the reservoir water level fluctuation.③It has a most adverse effect on the stability of Huangtupo landslide when the reservoir water level declining and short-time rainstorm. It may trigger the Huangtupo landslide resurrection.④Setting horizontal drainage holes in the leading edge of the landslide and ensuring the smooth flow of surface drainage network of the landslide. This will reduce the adverse effects of the reservoir water level and rainfall effects on the landslide. |
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